Mackle was born in Derrykeering, County Armagh. After school he attended Queen's University, Belfast, where he graduated with first class honours in chemistry in 1942, obtaining his PhD in 1947. He went to Magdalen College, Oxford, where he was awarded a second doctorate - a DPhil - in 1950. His field of study at Oxford centred on the structure of molecules in gases by electron diffraction, on which Mackle developed an international reputation.

In 1951 he returned to Northern Ireland to take up a post as lecturer in Physical Chemistry at Queen's University, where he specialised in thermochemistry. He designed and built aneroid rotating-bomb combustion calorimeters, used in thermochemical studies of organic sulphur-containing compounds. These were of great importance in petroleum refining, and in the pharmaceutical industry. He also was a dedicated and highly-regarded teacher, and his developments in his field he also utilised as teaching tools; he was able to use the results of his teaching and supervision to develop ideas in the fields of the historic evolution of valence theory and bond symbolism, including numerical aspects of chemical bonding, the mechanism of chemical bonding and its origins, chemical bonding in organic compounds, stereochemical aspects of chemical bonding, residual valence of unsaturated compounds, and electronic theories of valence. In 1962 he was promoted senior lecturer, and in 1964 was awarded the title of Reader. In addition, he was Warden of the Queen's University student residences at Queen's Elms from 1953-1963.

In 1958 he had been made a Fellow of the The Royal Institute of Chemistry; he published articles in journals including the Journal of the Chemistry Society and the Journal of Chemical Education. His wider outside interests were reflected in his having been a founder member (1961) of the Ulster Folklife Society, a member of the literature advisory panel of the Arts Council of Northern Ireland, and President of the Ulster Arts Club, 1970-1971. Also a keen athlete, he represented Irish Universities at tennis in 1951.

Born:	12 May 1921
Died:	30 July 1994